On 11/18/19 12:32 PM, mipri wrote:
Howdy,
The following program fails to compile if the second line
is uncommented:
import std;
void main() {
writeln([1, 2, 3].choice);
//writeln(['a', 'b', 'c'].choice);
}
Error: template std.random.choice cannot deduce function from argument
types !()(char[], MersenneTwisterEngine!(uint, 32LU, 624LU, 397LU, 31LU,
2567483615u, 11LU, 4294967295u, 7LU, 2636928640u, 15LU, 4022730752u,
18LU, 1812433253u)), candidates are:
/usr/include/dmd/phobos/std/random.d(2559): std.random.choice(Range,
RandomGen = Random)(auto ref Range range, ref RandomGen urng) if
(isRandomAccessRange!Range && hasLength!Range && isUniformRNG!RandomGen)
/usr/include/dmd/phobos/std/random.d(2569):
std.random.choice(Range)(auto ref Range range)
What is going on here? I get it that choice() isn't simply an algorithm
over T[], that there are some additional constraints, but surely a
char[] is just as random acc...
Nope, phobos treats a narrow character array (such as char[] or wchar[])
as a bidirectional range of dchar. It's called autodecoding, and it's
continually causing problems for about 10 years now.
....
Oh. It's because of emojicode.
unicode. I hope that was a joke ;)
This works:
import std;
void main() {
writeln([1, 2, 3].choice);
writeln(cast(char)(cast(uint8_t[])['a', 'b', 'c']).choice);
You could also use cast(dchar[]), and avoid the cast back to char.
-Steve
